This document describes the development of an airborne lidar instrument called A-LISTS to demonstrate technologies for a proposed spaceborne lidar mission called LIST. LIST aims to map global topography at 5m resolution to study Earth's surface and changes over time. A-LISTS will test a multi-beam laser transmitter, high sensitivity detectors, and data processing to achieve LIST measurement capabilities from an aircraft. Its first flight in September 2011 will collect lidar data over various terrain to evaluate performance. Key challenges for LIST that A-LISTS helps address include detecting ground returns through vegetation canopies and developing efficient, lightweight instruments.
1. Sixteen Channel, Non-Scanning Airborne Lidar Surface Topography (LIST) Simulator A.W. Yu, M.A. Krainak, D.J. Harding, J.B. Abshire, X. Sun, J.F. Cavanaugh, S.R. Valett, L. Ramos-Izquierdo, T. Winkert, C. Kirchner, M. Plants, T. Filemyr, B. Kamamia and W. Hasselbrack NASA Goddard Space Flight Center, Greenbelt, MD 20771 Paper: FR2.T03.3 IGARSS 2011, Vancouver, Canada 29 JULY 2011
2. Outline Introduction LIST Science Objectives & Requirements Lidar Measurement Approach & Performance Analysis Airborne Instrument Development Summary
44. A-LISTS Layout Rx Subsystem FIBER OPTIC BUNDLE Laser Telescope Keyboard/Mon Amplifiers BX PWR STRIP Video Recorder TIME CODE VIDEO Detector PS Support Frame MLA Pulse Gen+GPS Att. Align PWR STRIP Laser/TEC Ctl + Amp PS+ Chiller A/C Window DAS Lear Rack 2 Lear Rack 1
45. Boresight Alignment of the A-LISTS Transceiver Ground Testing Configuration 4x4 Fiber Bundle from Telescope Flight Configuration Start pulse from Tx Alignment of 16 channel Tx beams to 16 pixel IPA array with Autocollimator Laser output 7” Dia Rx Telescope 4x4 Fiber Bundle to Detector Array Rx Subsystem - IPD Output to 16 channel digitizer Laser Transmitter - [using pair of microlens arrays to generate a 4x4 pattern (patent pending)] A-LISTS Transceiver Enclosure on LearJet Fiber start pulse pickoff to receiver box Microlens arrays
46. IIP Airborne Footprint Velocity vector Yaw rotation of 14.5° yields uniformly spaced spots with 5 m horizontal spacing Geolocation accuracy of 1 m to assign return to correct 5 m pixel on ground 75 m Altitude = 10 km: Detector FOV = 7 m (0.7 mrad) Laser Spot = 5 m (0.5 mrad) Laser Spot Spacing = 20 m (2 mrad)
48. Single Channel Ranging Demonstration- Test Setup Cell Tower with Hard Target (1.5 km one way) Rx Telescope Intevac Single Element IPD Tx Telescope Multimode Fiber to Tx Telescope Start Pulse Detector GLAS Flight Spare Detector RSAS µchip Laser
49. Tower Target Board Returns Si APD output, single shot Target Board Return Start pulse leak through IPD output at 1/30 pulse energy, 7 shots overlaid Target Board Return HPMT dark counts and solar background counts Black: Averaged
50. Tower Target Board Return (Si APD & IPD) Si APD output pulse waveforms from the target board(~700 photons/pulse, 4ns FWHM) APD output (V) Sample number (at 0.2ns/sample) Laser shot number IPD output pulse waveforms from the steel tower structure IPD output pulse waveforms from the target board (~20 photons/pulse, 1ns FWHM) Back of the tower Front of the tower 20 ns (3m) IPD output (V) IPD output (V) Laser shot number Laser shot number Sample number (at 0.2ns/sample) Sample number (at 0.2ns/sample)
